A home base station is a base station used in a home. A home base station includes HeNB (Home enhanced Node B) used in Long Term Evolution (LTE) system and HNB (Home Node B) used in Universal Mobile Telecommunications System (UMTS). The architecture of HNB used in UMTS is shown in FIG. 1. Referring to FIG. 1, UE is connected to HNB via an Uu interface, the HNB is connected to HNB gateway (HNB GW) via an Iuh interface, and the HNB GW is connected to Servicing General Packet Radio Service (GPRS) Support Node (SGSN) in the core network (CN) via an Iu interface.
In the UMTS, there may be various types of HNBs, such as Open Access HNB, Hybrid HNB, and Closed Subscriber Group (CSG) HNB, so as to enrich the accessing services provided to user equipment (UE). Each CSG has a unique CSG identity (ID) for identifying the CSG. The Open Access HNB has no specific accessing UE, i.e., any UE can access the Open Access HNB. The CSG HNB allows specific UE it serves (hereinafter, referred to CSG UE for convenience) to access. The Hybrid HNB allows not only a CSG UE it serves to access so as to provide better service to the CSG UE, but also the other UEs which are not CSG UEs to access.
Currently, the relocation of the UE between the HNBs connected to a same HNB GW is carried out via SGSN. However, the burden of the CN is increased by relocation with SGSN, thereby resulting degrade of the relocation performance. A method of UE relocation which has been proposed is shown in FIG. 2. Referring to FIG. 2, the method includes the following:
Block 201: UE establishes an active Circuit Switch (CS) and/or Packet Switch (PS) session to CN via a source-HNB (S-HNB) and an HNB-GW.
Block 202: The S-HNB makes a decision to relocate the UE performing the CS and/or PS session.
Block 203: The S-HNB triggers relocation of the UE by sending a RANAP (Radio Access Network Application Part) Relocation Required message encapsulated in a RUA (RANAP User Adaptation) Direct Transfer message to the HNB-GW.
In this block, a target Radio network Control (RNC) identity, target HNB (T-HNB) Cell information and relocation information are included in the RANAP Relocation Required message.
Block 204: The HNB GW determines a T-HNB, and sends a RANAP Relocation Request message encapsulated in a RUA Connection message or a RUA Direct Transfer message to the T-HNB.
In this block, the HNB GW establishes a specific UE context identity used between the HNB and the HNB GW, and CSG membership status information may be included in the RUA Connection message.
After receiving the RANAP Relocation Request message, the T-HNB processes the RANAP Relocation Request message, and allocates suitable resources for the UE to be relocated.
Block 205: The T-HNB sends a RUA Direct Transfer message with the RANAP Relocation Request Acknowledge message encapsulated therein to the HNB GW.
Block 206: The HNB GW constructs a RANAP Relocation Command message, and sends it to the S-HNB by encapsulating it in a RUA Direct Transfer message.
Block 207: The S-HNB sends a Physical Channel Reconfiguration message to the UE.
Block 208: The UE sends Uplink Synchronization information to the T-HNB.
Block 209: The T-HNB sends a RANAP Relocation Detection message encapsulated in a RUA Direct Transfer message to the HNB GW.
Block 210: The UE sends a Physical Channel Reconfiguration Complete message to the T-HNB.
Block 211: The T-HNB sends a RANAP Relocation Complete message encapsulated in a RUA Direct Transfer message to the HNB GW.
Block 212: The HNB GW constructs a RANAP Iu Release Command message, and sends the RANAP Iu Release Command message encapsulated in a RUA Direct Transfer message to the S-HNB.
Block 213: The S-HNB acknowledges the Iu release procedure by sending a RUA Disconnect message encapsulated with a RANAP Iu Release Complete message to the HNB GW.
Block 214: The HNB GW deregisters the UE from the S-HNB, and the S-HNB releases the resources allocated to the UE, and releases all context information of the UE stored therein.
In this block, the UE deregistration may be initiated by the S-HNB or by the HNB GW.
It is to be noted that, if only CS or only PS exists, blocks 202-213 will be performed once; if both CS and PS exist, blocks 202-213 will be repeated. For a specific UE, when blocks 202-213 are repeated, the UE is not reallocated with a new UE context identity. When block 204 is performed for the first time, the RANAP Relocation Request massage is sent to the T-HNB via the RUA Connection message, while when block 204 is performed again, the RANAP Relocation Request may be sent to the T-HNB via a RUA Direct Transfer message. Alternatively, when block 204 is performed again, the RANAP Relocation Request may be sent to the T-HNB via the RUA Connection message, just without reallocating the UE context identity.
Therefore, the whole procedure of the enhanced UE relocation method in prior art is completed.
It can be seen from the above procedure that, in the enhanced UE relocation method, the interaction with the CN is decreased, thereby reducing the burden of the CN. However, since the carrying information and security context information of the UE are not included in the RANAP Relocation Required message in the relocation procedure, a large amount of the context information should be stored in the HNB GW, also, the HNB GW must reconstruct information associated with the relocation in the relocation procedure, thereby increasing the complexity of the HNB GW.
In addition, the user plane data transport between the HNB and the CN may be carried out with one tunnel or two tunnels. When one tunnel is used, the user plane data transport is carried out from the HNB to the CN directly or from the CN to the HNB directly, without passing through the HNB GW. When two tunnels are used, the user plane data transport is carried out from the HNB to the HNB GW and then to CN, or from the CN to the HNB via the HNB GW. When the user plane data transport is carried out with two tunnels, the relocation procedure may be as shown in FIG. 2. When the user plane data transport is carried out with one tunnel, how to notify the CN of the change of the downlink user plane bear transport path is a problem to be solved.
Furthermore, the existing optimized relocation procedure makes all relocation signaling to be terminated at HNB GW, so as to avoid interaction with the CN. However, the T-HNB does not know whether or how to carry out the optimized relocation procedure, and thus the problems, such as quality of service (Qos) negotiation, partial Radio Access Bear (RAB) establishment failure and security algorithm selection, in the optimized relocation procedure cannot be solved.
Finally, when the UE is in a cell forward access channel (cell_FACH) state, how to support the optimized relocation procedure, how to perform access control, and how to construct a Relocation Required message by the S-HNB cannot be solved by the existing optimized relocation procedure.